A warehouse has only the loading dock manned by a three$-$person crew. Trucks arrive at the loading dock at an average rate of $4$ trucks per hour and the arrival rate is Poisson distributed. The loading of a truck takes $10$ minutes on an average and can be assumed to be exponentially distributed. The operating cost of a truck is Rs$\mathrm{.}20$ per hour and the members of the crew are paid @ Rs$\mathrm{.}6$ each per hour. Would you advice the truck owner to add another crew of three persons? $(8)$